Typically, permanent magnet direct current electric motors for power tools have a frame, an armature including the core and associated windings, and commutator and brush assemblies. The frame can be formed from a soft iron or steel yoke or can of open cylindrical shape mounted on a bearing base plate and closed at its top end by a cap plate. A rectifier can be provided for DC motors to convert alternating current into direct current for application to the coils of the armature mounted within the yoke. The rectifier is typically mounted remotely from the motor housing or to the outside of the housing, such as to a cap plate. Such a "can" type DC motor is assembled in a separate operation before being incorporated into the power tool with which it is to be used. Such preassembly or separate assembly operation gives rise to significant motor-related manufacturing costs. A second assembly operation is required to assemble the internal components of the power tool, including the preassembled motor, in the power tool housing. Thus, it is desirable for a power tool to be provided with a DC motor which does not require a separate assembly operation therefor and which can be incorporated into the assembly operation for the power tool itself.
U.S. Pat. No. 5,349,785 discloses a motor pre-assembly utilizing a support member onto which the armature is mounted by screwing down a lower roller bearing in a bearing well formed in the support member and through which one of the armature shaft ends is inserted. Additionally, the switch, printed circuit board, power cord and wiring are secured to the support member. With the armature secured to the plate by frictional forces between the shaft end and lower bearing, the motor support is turned upside down so as to be lowered into an upwardly opening bucket-shaped motor housing so that the other end of the armature shaft is aligned with and extends into an upper bearing secured in its bearing well formed in the bucket-shaped housing. The motor preassembly to the motor support member requires an extra manufacturing step and increased costs associated therewith. Incorporation of the motor pre-assembly into the polisher assembly also requires a careful alignment of the motor support carrying the armature during such assembly so that its shaft properly fits into the upper bearing when the armature is stacked in the bucket-shaped housing. In addition, the use of screws to secure the various internal components to the support increases the time, expense and complexity of assembly of the motor.
Besides the manufacturing costs associated with the separate assembly of "can" type DC motors, another problem with these motors is that provision must be made for the output leads on the rectifier such that they can be electrically connected to the brushes to supply direct current power to the armature coils. Generally, the rectifier is mounted near or on the frame as previously mentioned such that the leads must pass through the motor housing, such as through slots or apertures in the cap of the yoke. In another known direct current motor assembly, the top cap mounts a modified rectifier assembly which extends on either side of the cap so as to obviate the need to provide slots or apertures in the cap for the rectifier assembly leads. In both types of motor assemblies, specially dedicated structures, i.e., apertured caps and/or modified rectifier assemblies, must be provided to accept or accommodate the leads extending from the rectifier to the brushes.